The present application is directed to methods of moving a media sheet and more specifically to moving a media sheet at a constant speed across a scanner in a scanning device.
Many scanning devices utilize an automatic document feeder to feed media sheets across a stationary scan head. The automatic document feeder provides a quick and easy solution for scanning documents. One challenge is maintaining a constant velocity of the media sheet as it is scanned. Sudden variations in the speed may cause an image quality defect such as a line compression or expansion.
Most automatic document feeders incorporate a pick and separation mechanism designed to pick only one media sheet at a time. In one embodiment, a top sheet in a media stack is picked and fed into the media path, and the separation mechanism prevents feeding additional media sheets. The separation mechanism may be stopped as the top sheet continues to be fed along the media path. A force created between belts and/or rollers in contact with the media sheet places a load on the media sheet as it moves along the stopped mechanism. This load is released when the trailing end of the media sheet moves beyond the separation mechanism. The release causes an increase in a rotation speed of feed rollers that are moving the media sheet along the media path. This increase in speed causes a sudden velocity increase in the media sheet as it moves along a length of the media sheet. If the media sheet is being scanned during the load release, the velocity increase causes an image quality defect.
The media path should be constructed to ensure accurate scanning of the media sheet occurs as it moves along the media path. Further, the media path should be constructed to prevent media jams that may occur during the pick and feeding process. The media jams require that the scanning device be deactivated, the media path accessed, and the jammed media sheet removed. This process is frustrating for users, greatly slows throughput of the device, and may result in damage to the media sheet and/or scanner.